1. Field of the Invention
The present invention relates to a glass manufacturing container, a glass manufacturing apparatus with the same and a glass manufacturing method using the glass manufacturing apparatus, and particularly relates to a glass manufacturing container including a container body made of a precious metal or an alloy containing a precious metal, a glass manufacturing apparatus with the same and a glass manufacturing method using the glass manufacturing apparatus.
2. Description of Related Art
Conventionally, there is generally used, as an industrial glass manufacturing method, a method including the steps of: melting glass raw material; refining the molten glass; and forming the refined molten glass. Examples of a container for manufacturing glass include a container made of a refractory and a container made of Pt or an alloy containing Pt.
In manufacturing glass not required to have very high grade in terms of foreign substances and bubbles, such as window glass, a container made of a refractory is sometimes used as a container for manufacturing glass. On the other hand, in manufacturing glass required to have high grade in terms of foreign substances and bubbles, such as substrate glass for LCDs or like displays, a container made of a precious metal, such as Pt, Ir or Rh, or an alloy containing a precious metal, such as Pt, Ir or Rh, is generally used. The reason for this is that when a container made of a precious metal, such as Pt, Ir or Rh, or an alloy containing a precious metal (hereinafter referred to as a “precious metal container”) is used for glass manufacturing, foreign substances and the like are less likely to be mixed from the container into molten glass.
However, when a precious metal container is used for glass manufacturing, bubbles due to water in glass may be formed on the surface of the precious metal container facing molten glass. The reason for the formation of bubbles can be attributed to the fact that hydrogen produced by decomposition of water contained in the glass passes through the precious metal container and is then released to the outside, whereby the oxygen concentration of the molten glass located near the surface of the precious metal container increases. More specifically, it can be assumed that hydrogen gas produced by the reaction represented by the following formula (1) passes through the precious metal container and is then released to the outside, while oxygen not passing through the precious metal container is left in the molten glass located near the surface of the precious metal container, whereby the oxygen concentration of the molten glass located near the surface of the precious metal container increases and bubbles are thereby formed.OH−→½O2+½H2+e−  (1)
In view of this problem, for example, Patent Documents 1 to 5 listed below propose methods that can reduce the formation of bubbles due to water in glass when a container made of Pt or an alloy containing Pt (hereinafter referred to as a “Pt container”) is used.
For example, Patent Document 1 below describes a method for reducing the formation of bubbles due to water in glass by reducing the β-OH value of the glass to less than approximately 0.5/mm.
Patent Document 2 below describes a method for reducing the formation of bubbles due to water in glass by controlling, during glass manufacturing, the partial pressure of hydrogen on the outside of the Pt container relative to the partial pressure of hydrogen in the Pt container.
Patent Documents 3 and 4 below describe a method for reducing the formation of bubbles due to water in glass by applying a glass barrier coating on the outer surface of the Pt container to reduce the hydrogen permeability of the Pt container.
Patent Document 5 below describes a method for reducing the formation of bubbles due to water in glass by forming, on the outer surface of the Pt container, a layer made of alumina-based ceramic particles containing 0.2% to 5% by weight of Fe, in terms of Fe2O3, relative to the total amount of alumina-based ceramic particles and having a changing point, at which the Fe redox ratio increases, within the temperature range of molten glass.